The access technique of an uplink of Long Term Evolution (LTE), of which standardization in 3rd Generation Partnership Project (3GPP) is in a convergence phase, adopts Single Carrier-Frequency Division Multiplexing Access (SC-FDMA). Additionally, with a configuration of transmitter for performing a subcarrier mapping in a frequency domain, the above access technique is also referred to as Discrete Fourier Transform-Spread-Orthogonal Frequency Division Multiplexing (DFT-S-OFDM).
As the reason why SC-FDMA is adopted, it can be listed that coverage can be enlarged because Peak to Average Power Ratio (PAPR) is small. Additionally, with the allocation of resource blocks in SC-FDMA, only the resource blocks (RB) that are continuous in a frequency axis are allocated. Herein, the resource block is configured of a plurality of subcarriers, and one resource block is configured of 12 subcarriers in LTE.
A Constant Amplitude Zero Auto-Correlation (CAZAC) sequence characterized in that PAPR is small is adopted as reference signals of the LTE uplink. The CAZAC sequence is a sequence of which amplitude is constant in both the time domain and the frequency domain, and yet of which an auto correlation value is zero except for a phase difference being zero. PAPR of the CAZAC sequence is suppressed at a small level because the amplitude is constant in the time domain, and yet the CAZAC sequence is suitable for estimating channels in the frequency domain because the amplitude is constant also in the frequency domain. The sequence number of the CAZAC sequence depends upon a sequence length thereof. For example, there exists a Zadoff-Chu sequence that is represented by Equation 1 adopted in LTE as one of the CAZAC sequences (see Non-Patent literature 1).cqL(n)=exp(−jπqn(n+1)/L)n=0, . . . ,L−1  (Equation 1)
In the Zadoff-Chu sequence, it is when the sequence length becomes a prime number L that the sequence number is maximized, and the sequence length thereof becomes L−1. In LTE, the sequence obtained by subjecting the Zadoff-Chu sequence having a prime number length to cyclic extension is employed in order to secure the sequence number of the CAZAC sequence. As shown in FIG. 1, the cyclic extension technique is a technique of extending the sequence length of the Zadoff-Chu sequence in the frequency domain to the number of the subcarriers of data signals. Employing the cyclic extension technique makes it possible to secure many kinds of the sequence lengths without largely damaging properties of the above-described CAZAC sequence. Hereinafter, the reference signal sequence to be employed for LTE is described as the CAZAC sequence.
The specification of LTE specifies 30 kinds of CAZAC sequence groups including the CAZAC sequence each having a different sequence length, and allocates one CAZAC sequence group in each cell. Additionally, when the CAZAC sequence group differs, the different CAZAC sequence is employed without fail because one CAZAC sequence belongs only to one certain CAZAC sequence group. Further, in the current situation, the sequence length that the CAZAC sequence groups support is 20 MHz, being a maximum bandwidth of LTE, or less.
Non-PATENT LITERATURE 1: B. M. Popovic, “Generalized Chirp-Like Polyphase Sequences with Optimum Correlation Properties,” IEEE Tansactions on Information Theory, Vol. 38, No. 4, pp 1406-1409, July 1992.